Phased antenna arrays are a popular means for generating a configurable antenna radiation pattern for wireless transmission or reception. A narrow beam antenna radiation pattern can be formed using an array of antenna elements in cooperation with phase shifters. The antenna elements are operated in a coherent manner so as to focus the beam in a desired direction. Beamforming and beam steering using this approach is widely known in the art. However, gain and phase mismatches among elements of the antenna array can impact performance. For example, Ming-Da Tsai and Arun Natarajan, “60 GHz Passive and Active RF-path Phase Shifters in Silicon,” 2009 IEEE Radio Frequency Integrated Circuits Symposium reports a typical 3° RMS error or maximum 10° error for phase shifters operating in the 60 GHz frequency range. Phase and gain variation among phase shifters and amplifiers can be temperature dependent and/or introduced as an artifact of the manufacturing process.
One technique for calibrating phased array antennas is described in Herbert F. Aumann et al., “Phased Array Antenna Calibration and Pattern Prediction Using Mutual Coupling Measurements,” IEEE Transactions on Antennas and Propagation, vol. 37, No. 7, July 1989, pp. 844-850. This reference is hereinafter referred to as Aumann. This approach utilizes the inherent mutual coupling in an array to both calibrate and predict the radiation patterns. Other techniques for far field array calibration involve the use of calibration chambers, or the use of far field sampling points as in radar applications. However, existing calibration techniques call for specialized equipment and/or a dedicated calibration process, during which the antenna is not available for communication operations.
Therefore there is a need for a method and apparatus for antenna array beamforming calibration, that obviates or mitigates one or more limitations of the prior art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.